U.S. patent number 5,102,628 [Application Number 07/196,288] was granted by the patent office on 1992-04-07 for riser simulator.
This patent grant is currently assigned to The University of Western Ontario. Invention is credited to Hugo I. De Lasa.
United States Patent |
5,102,628 |
De Lasa |
April 7, 1992 |
Riser simulator
Abstract
An apparatus for testing performance of a catalyst in a gaseous
phase catalytic reaction for a given reactant comprises a reactor
receiving a predetermined quantity of fluid reactant discharging
the reaction mixture, including reaction products, from the reactor
after a predetermined residence time. The reactor comprises a
confined reactor volume with an upflow zone and a downflow zone. A
device circulates fluids upwardly through the upflow zone and
downwardly through the downflow zone where particulate catalysts in
the upflow zone are fluidized by the upward flow of the fluid. The
circulating device is adapted to circulate the fluid about the
reactor volume at a rate which provides at any moment during the
residence time for the reactants an essentially uniform
concentration of reactants throughout the reactor volume to
simulate conditions in a catalytic riser reactor.
Inventors: |
De Lasa; Hugo I. (London,
CA) |
Assignee: |
The University of Western
Ontario (Ontario, CA)
|
Family
ID: |
4135719 |
Appl.
No.: |
07/196,288 |
Filed: |
May 20, 1988 |
Foreign Application Priority Data
Current U.S.
Class: |
422/140; 422/139;
422/144; 422/227; 422/228; 422/239; 422/269; 436/37 |
Current CPC
Class: |
B01J
8/24 (20130101); G01N 31/10 (20130101); B01J
2208/00407 (20130101); B01J 2208/00876 (20130101); B01J
2208/00884 (20130101); B01J 2208/00522 (20130101) |
Current International
Class: |
B01J
8/24 (20060101); G01N 31/10 (20060101); B01J
008/20 (); G01N 031/10 (); F27B 015/20 () |
Field of
Search: |
;422/139,140,144,227,228,239,206,261,269,275 ;436/37 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Warden; Robert J.
Assistant Examiner: Santiago; Amalia L.
Attorney, Agent or Firm: Shoemaker and Mattare, Ltd.
Claims
I claim:
1. An apparatus comprising a reactor vessel, means for introducing
a predetermined quantity of fluid reactant into said reactor
vessel, means for withdrawing a reaction mixture including reaction
products from said reactor vessel after a predetermined residence
time for reactants in said reactor vessel, said reactor vessel
comprising means defining a confined reactor volume with an upflow
zone and a downflow zone, means in said reactor volume for
continuously circulating fluids in said reactor volume upwardly
through said upflow zone and downwardly through said downflow zone,
means for containing in said upflow zone a predetermined quantity
of particulate catalyst, thereby defining said confined reactor
volume, said containing means having a screen inlet and a screen
outlet, said containing means being of sufficient volume to permit
fluidization of said particulate catalyst in said containing means
by said fluid flowing upwardly therethrough to form a fluidized bed
of catalyst particles, said circulating means being located above
said screen outlet to induce a uniform upward flow of fluid through
said containing means, said circulating means circulating said
fluid about said reactor volume at a rate which provides at any
moment during said residence time for such reactants an essentially
uniform concentration of reactants through said reactor volume to
simulate thereby conditions in a catalytic riser reactor, said
circulating means being associated with means to circulate reactant
fluid at said rate prior to said reactant introduction means
introducing reactant fluid to said reactor.
2. The apparatus of claim 1, wherein said reaction mixture
withdrawal means withdraws such reaction mixture form said reactor
and transfers such reaction mixture into an environment which
essentially immediately ceases further reaction.
3. The apparatus of claim 2, further comprising means for analyzing
reaction product composition and means for delivering said
withdrawn reaction mixture from said withdrawal means to said means
for analyzing reaction product composition.
4. The apparatus of claim 1, wherein said introduction means
includes means for passing an inert carrier gas through said
reactor prior to introduction of fluid reactant, said circulating
means being capable of circulating such inert gas through said bed
of catalyst particles to fluidize such particles prior to said
introduction means introducing fluid reactants to said reactor,
means for stopping said means for passing a carrier gas through
said reactor during said residence time of said fluid
reactants.
5. An apparatus for testing performance of a catalyst in a gaseous
phase catalytic reaction for a given reactant, said apparatus
comprising
a fluidized bed reactor, said reactor having a vessel and means for
heating a wall of the vessel, said reactor further including an
inlet and an outlet,
means defining an upflow zone and an adjacent downflow zone within
said vessel,
said means defining said upflow zone comprising an annular baffle
with means for supporting said annular baffle centrally of said
reactor vessel,
said annular baffle defining a hollow vertically extending core
with a lower end and an upper opening,
an inlet screen being provided at said lower opening and an outlet
screen being provided at said upper opening,
said hollow core providing sufficient volume for fluidization of a
particulate catalyst being tested, at lest one of said inlet screen
and outlet screen being removable to permit placement of a catalyst
being tested within said hollow core,
means located above said upflow zone for circulating fluid upwardly
of said upflow zone and downwardly of said downflow zone,
said circulating means being a revolving impeller located above
said outlet screen,
said impeller withdrawing fluid reaction mixture from said upflow
zone and redirecting it downwardly in said downflow zone,
means for conducting an inert carrier gas to and away from said
vessel via said inlet and outlet,
means for controlling flow of inert carrier gas through said
conducting means,
means for injecting a predetermined volume of fluid reactants into
said conducting means,
said flow control means stopping flow of inert carrier gas once an
injected predetermined volume of fluid reactants has entered said
reactor vessel,
means for withdrawing reaction products from said reactor vessel
via said outlet with said flow control means resuming flow of inert
carrier gas after a predetermined residence time for such fluid
reactants in said reactor vessel, said withdrawal means withdrawing
such reaction product into an environment which essentially
immediately ceases further reaction,
said reactor vessel having a cylindrical reactor chamber,
said annular baffle having an outer cylindrical wall spaced form an
inner wall of said reactor chamber to define an annular section for
said downflow zone,
said annular section being of limited volume to provide for rapid
recirculation of fluids emerging from said outlet screen back to
said inlet screen of a fluidized bed of particulate catalyst to
provide at any moment during residence time of fluid reactants in
said chamber an essentially constant concentration of reactants in
said reactor chamber, and thereby simulate conditions in a
catalytic riser reactors,
means for rotating said impeller, said impeller circulating said
flow of fluid upwardly through said cylindrical-shaped reactor
chamber in a uniform manner, and
means for mounting a plurality of radially directed baffles in said
outer cylindrical wall of said annular baffle to minimize swirling
of redirected fluid reaction mixture in said downflow zone.
6. The apparatus of claim 5, further comprising means for
vaporizing fluid reactants, said vaporizing means being upstream of
said injection means and being fluidly connected thereto.
7. The apparatus of claim 5, further comprising means for heating
injected fluid reactants in said conducting means with carrier gas
to a predetermined elevated temperature, said control means being
operable to stop flow of said carrier gas when injected fluid
reactants enter said heating means, said control means being
capable of resuming flow of said carrier gas to introduce such
heated fluid reactants to said reactor when such heated fluid
reactants are at such predetermined temperature.
8. The apparatus of claim 5, wherein said withdrawal means
transfers withdrawn reaction mixture including reaction products
form said reactor vessel to means for analyzing reaction product
composition.
9. The apparatus of claim 5, wherein said injecting means injects a
predetermined quantity of oxygen into said conducting means to
regenerate during such predetermined residence time a coked
catalyst.
Description
FIELD OF THE INVENTION
This invention relates to testing apparatus and method for
determining the performance of a catalyst in a gaseous phase
catalytic reaction or during regeneration.
BACKGROUND OF THE INVENTION
The art of catalytic cracking reactions has evolved considerably
over the past fifteen to twenty years. It was common to employ a
fluidized bed of catalyst particles in the catalytic cracking of
petroleum feed stock to form desired light oils, gasolines,
solvents and the like. Although it is possible with existing
testing equipment to predict how a particular catalyst will behave
with a given feedstock, the advances in the field of catalytic
cracking has led to reactor designs which cannot be predicted by
existing test units. There is a considerable lack of suitable
reaction data for modelling and simulating the more advanced
industrial scale riser catalytic cracking reactor which has typical
contact times in the range of two to twenty seconds. There is
significant uncertainty as to how to predict performance of
industrial scale riser reactors. Hence the use of this technology
in the petrochemical industry is severely hindered by the limited
data and understanding of fast catalytic cracking reactions of
different feedstocks in combination with various catalysts. It is
this very data that the technical staff of a refinery needs to make
crucial decisions about possible changes in operating conditions,
modification of existing units, scaling up, processing of different
feedstocks depending upon the source of supply, change of the
catalysts, adaptation of the process to new conditions of the
ever-changing gasoline market and other like considerations.
The same lack of relevant data applies to the regeneration of
cracking catalysts under the conditions of riser regenerators. This
is also a crucial matter, because the combustion of coke has a
significant influence on the overall thermal balance of an
industrial scale refinery. The endothermic heat consumed by the
cracking reaction is normally supplied by the heat generated by the
coke combustion.
Data about the fast regeneration of cracking catalysts is required
to develop new cracker-regenerator configurations where both the
regenerator and the cracker are transport line reactors. Several
technical advantages can be claimed for transport line
regenerators--uniform in control in coke levels in the catalyst at
the regenerator exit, improved catalyst performance and selectivity
and higher zeolite structure stability.
As mentioned, there are a variety of laboratory scale testing units
available to determine the activity of selected catalysts and their
effect on catalytic cracking of various feedstocks. An example of
such a testing unit is disclosed in U.S. Pat. No. 4,419,328. This
patent discloses a conventional fluidized bed controlled by a
computer. A continuous flow of hydrocarbons is fed to the unit. In
this unit, there is only a similarity between the reactant
residence time (few seconds) whereas the catalyst time on stream is
300 seconds to 10,000 seconds. This is a major problem for a true
modelling of riser reactors. The patent discloses that the
fluidized bed of the reactor is fed with a continuous flow of
hydrocarbons that produce fluidization. If the flow is stopped, the
bed is defluidized without any continued contacting of the
catalysts with the introduced hydrocarbons. Moreover even during
the continuous operation of the reactor, no uniform residence time
can be secured for the hydrocarbon molecules in the fluidized bed.
There is significant dissimilarities existing between the time the
reactant molecules contact the catalyst and the time the catalyst
is exposed to the reacting hydrocarbon environment. As a result,
this system could not in any way adequately simulate the conditions
of a riser reactor.
Refiners commonly employ a microactivity test unit to establish the
activity of catalysts for particular feedstocks. In conventional
fluidized bed processes and the like, such units can be very
valuable in saving the refiner millions of dollars per year in
product value by predicting the effectiveness of the catalyst used
in the cracking unit. The microactivity test unit (MAT) is based on
the concept of continuously contacting a hydrocarbon feedstock with
a catalyst sample of approximately one gram during a 75 to 100
second residence time. The procedure is defined in ASTM (D3907-80).
In the MAT test, the catalyst/oil ratio is defined on a cumulative
basis which means that the C/O ratio is obtained after a mass of
catalyst contacts a hydrocarbon flow for about 75 to 100 seconds.
Then in the MAT apparatus, the C/O ratio depends on the catalyst
time-on-stream. This results in a significant difference with the
conventional riser reactor units, where the catalyst flow and
hydrocarbon flow are set for a given operating condition and the
catalyst/oil ratio is not a function of a catalyst
time-on-stream.
Another significant difference between the MAT and the riser
reactor is with respect to contact times. In a conventional riser
reactor, the catalyst and the hydrocarbon stay in intimate contact
for about two to twenty seconds before being separated in cyclones.
In the MAT unit, however, the catalyst reacts with hydrocarbons for
about 75 to 100 seconds.
Additional differences can be found between the riser and MAT unit
in the way coke is laid down on the catalyst. While in the riser,
the coke concentration is only the function of catalyst residence
time, in the MAT the coke concentration depends on both the bed
axial position and catalyst time-on-stream. Consequently, in the
MAT the interpretation of coke deactivation effects and catalytic
cracking data is very complex.
This information demonstrates that the MAT technique only allows
one to establish relative performance of catalytic materials and is
of questionable application or extrapolation to catalytic riser
reactors. The kinetic models derived from the data obtained using
the MAT are of little use for effectively simulating riser reactors
and scaling up thereof.
In accordance with this invention, a testing unit and method is
provided which simulates the reaction conditions in a catalytic
riser reactor. The system may be used to accurately predict the
activity of a catalyst for a given feedstock as well as the
conditions of regenerating catalysts.
SUMMARY OF THE INVENTION
According to an aspect of the invention, an apparatus for
evaluating processing conditions in the presence of a particulate
catalysts comprises a reactor, means for introducing a
predetermined quantity of fluid reactant into the reactor and means
for withdrawing a reaction mixture including reaction products from
the reactor after a predetermined residence time for reactants in
the reactor. The reactor comprises a confined reactor volume with
an upflow zone and a downflow zone. Means in the reactor volume is
provided for continuously circulating fluids in the reactor volume
upwardly through the upflow zone and downwardly through the
downflow zone. Means for containing in the upflow zone a
predetermined quantity of particulate catalysts is provided. The
containing means has a screen inlet and screen outlet. The
containing means is of sufficient volume to permit fluidization of
the particulate catalyst in the containing means by the fluid
flowing upwardly therethrough to form a fluidized bed of catalyst
particles. The circulating means is adapted to circulate the fluid
about the reactor volume at a rate which provides at any moment
during the residence time for the reactant an essentially uniform
concentration of reactants throughout the reactor volume to
simulate thereby conditions in a catalytic riser reactor. The
circulating means circulates reactant fluid at the prescribed rate
immediately upon the reactant introduction means introducing
reacting fluid to the reactor.
According to another aspect of the invention, a method for testing
performance of a catalyst for a gaseous phase catalytic reaction
conducted in a conventional riser reactor comprises developing a
fluidized bed of a predetermined quantity of catalyst particles to
be tested in a reactor chamber. The chamber has an upflow zone in
which the catalyst particles are fluidized by a flow of inert gases
and a downflow zone. The gases are circulated through the upflow
and downflow zone. Gaseous reactants are introduced at a
predetermined temperature into the reactor and then flow into the
reactor is closed off to retain the reactants in the reactor. The
catalyst particles are maintained around a predetermined
temperature. The reactants react in the presence of the catalyst to
produce a reaction mixture including reactant products. The
reaction mixture is recirculated rapidly through the downflow zone
to provide at any moment during the catalytic reaction an
essentially constant reactant concentration in the reactor chamber
to simulate catalytic reaction conditions in the conventional riser
reactor. The reaction mixture is retained in the reactor chamber
for a predetermined residence time. The reaction mixture is
withdrawn from the reactor chamber after the predetermined
residence time is expired, into an environment which essentially
immediately ceases further reaction. The reaction mixture is
analyzed for reaction product composition to determine activity of
the catalyst at the predetermined temperature for the catalyst
bed.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments of the invention are shown in the drawings,
wherein:
FIG. 1 is a schematic view of the testing unit; FIG. 2 is a
perspective view of the reactor of the test unit of FIG. 1;
FIG. 3 is an exploded section through the reactor of FIG. 2;
FIG. 4 is a top view of a section of the reactor of FIG. 2;
FIG. 5 is a section through the sealing jacket for the impeller
shaft;
FIG. 6 is a plot of conversion of gas oil versus catalyst to oil
(C/O) ratio (error bars are similar to the ones shown for all
curves);
FIG. 7 is a plot of yields of gasoline, light gases plus coke and
unconverted gas oil at 500 C versus C/O ratio (darkened symbols
refer to 5 seconds reaction time, open symbols for 10 seconds);
FIG. 8 is a plot of yields of gasoline, light gases plus coke and
unconverted gas oil at 550 C versus C/O ratio (darkened symbols
refer to 5 seconds reaction time, open symbols for 10 seconds);
and
FIG. 9 is a plot of selective to gasoline versus C/O ratio.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The test unit, according to a preferred aspect of the invention,
will be exemplified with respect to testing performance of
catalysts in cracking reactions conducted in catalytic riser
reactors. Also, the effectiveness in decoking (regenerating) the
catalyst will be demonstrated with this test unit. It is
appreciated that a variety of catalytic reactions of similar
conditions may also be readily tested in this unit while employing
the principles of the invention to be exemplified hereinafter.
With reference to FIG. 1, a schematic of an exemplary test unit is
shown. The test unit generally designated 10 has a reactor 12. A
carrier gas in the form of helium is supplied by cylinder 14. When
the test unit is used to determine the effectiveness of the
predetermined catalyst for a given feedstock, the injector system
16 is used to inject into the carrier gas a predetermined quantity
of hydrocarbon feedstock material. A constant temperature enclosure
or box 18 is provided which has a preset temperature. The heater
box 18 is used to maintain the hydrocarbon sample at a
predetermined temperature before introduction to the reactor 12.
All flows of fluids through the various conduits are controlled by
two valves 20 and 22. Valve 20 controls the admission of fluids to
the reactor 12, whereas valve 22 controls the withdrawal of fluids
from the reactor 12. Presence of hydrocarbons in incoming and
outgoing streams of reactants and reaction products are determined
within thermal conductivity measuring system 24 having thermal
conductivity measuring devices 26 and 28. The temperatures, as
indicated by electrical signals generated in sensors 26 and 28, are
fed to an analog to digital converter 30 which in turn has an
output to microprocessor 32 for recordal of relevant data. The
reaction mixture, as withdrawn from the reactor 12, is fed to a gas
chromatograph 34 for analysis of the product composition. The
output of the gas chromatograph is then fed to the integrator 36
for printout of the results.
The testing unit is set up to test hydrocarbon feedstock as would
be injected by the injector box 16. The temperature of the injector
system is set at approximately 150.degree. C. A pump is provided in
the injector system to circulate the hydrocarbon feedstock to
provide a homogeneous hydrocarbon sample. The thermal conductivity
detectors 26 and 28 are brought to a temperature of approximately
350.degree. C. while the temperature of the coil constant
temperature enclosure 18 and the valves 20 and 22 are heated to a
temperature of approximately 300.degree. C. The temperature of the
reactor 12 is set and controlled at the level chosen for the test
run. Heating tapes or the like may be used to heat the various
conduits of the system while adequate sensors are employed to
monitor the temperature in the lines. The temperature selected for
the lines may be in the range of 300.degree. C. to 400.degree.
C.
The inert helium carrier gas from tank 14 flows through filter 38
and mass flow controller 40. The helium flows through line 42 which
passes through the non-sensing side of the thermal conductivity
detector 28 and also through the non-sensing side of the thermal
conductivity detector 26 before flowing through to the valve 44 for
the injector system 16. The valve 44 is also connected to an oxygen
supply tank 46 which supplies oxygen in the catalyst regeneration
cycle which will be discussed with respect to another embodiment of
the invention.
The inert carrier gas continues to flow through line 48 into the
injector system 16. The carrier gas exits the injector system via
line 50 which passes through the sensing side of thermal
conductivity detector 26 and into valve 20 via port 5. For the
first position of the valve 20, port 5 is connected to port 1 to
deliver the inert gas via line 52 into coil 54 and then through
line 56 into the inlet 58 of the reactor 12. The inert carrier gas
emerges through outlet 60 of the reactor 12 to valve 22 at port B
via line 62. For the first position of valve 22, port B is
connected to Port A to deliver the carrier gas via line 64 back to
valve 20 at port 2. For the first position of the valve 20, port 2
is connected to port 6 to deliver the gas via line 66 through the
sensing side of thermal conductivity detector 28 to the gas
chromatograph 34.
Once all temperatures in the test system have reached steady state
and the heaters 68 for the reactor are also at steady state, a
sample feedstock of hydrocarbon may be injected into the carrier
stream. At this point, adequate current for the thermal
conductivity detector is selected. At the same time, the other
components of the data acquisition system including the
Hewlett-Packard 6940 Multiprogrammer and Hewlett-Packard 9826
microprocessor are in the ready condition. A valve, not shown, for
the feedstock injection system is switched to the load position in
order to introduce into the inert helium gas stream of inlet line
48 a hydrocarbon pulse of approximately 2 microliters. The
hydrocarbon pulse is immediately vaporized in the heated injection
system and carried by the helium through line 50 towards the
sensing side of thermal conductivity detector 26.
Once the pulse size and shape are determined by the thermal
conductivity detector 26, the hydrocarbon feedstock sample
continues its circulation through line 50 to valve 20, then via
port 1 into the coil 54 of the coil heater system 18. At this point
in the run, the valve 20 is switched to a second position, such
that ports 1 and 3 are connected and ports 2 and 4 are connected.
Delay of about five seconds is required between the hydrocarbon
injection and the switching of the valve 20 to the second position
to trap all hydrocarbon sample in the heater coil 54.
In changing the position of valve 20 to the second position, this
modifies the operation of the testing unit from the continuous mode
to the discontinuous mode of operation for the reactor. The reactor
unit is then isolated from the remainder of the set up. The inert
carrier gas continuously circulates through the thermal
conductivity detectors 26 and 28 the injector system 16 and the gas
chromatograph 34. This is achieved because the valve 20 in its
second position provides for interconnection of ports 5 and 6. The
inert carrier gas then circulates without interruption, thereby
keeping the operation of the thermal conductivity detectors and the
gas chromatograph unit under steady state operation, minimizing
oscillations or changes in the output signals of these
instruments.
With the hydrocarbon sample positioned in coil 54, the sample is
ready for injection into the reactor which is heated to a desired
temperature in the range of 500.degree. C. to 700.degree. C. To
accomplish this, the helium container 70 is connected to port 3 of
valve 20 by an additional valve 72. With valve 20 in the second
position, port 3 is connected to port 1. Valve 72 is therefore
opened and the hydrocarbon sample in coil 54 is immediately fed
into the reactor 12. Intense mixing occurs in the fluidized bed of
the reactor 12 where all catalyst particles are essentially
surrounded by a hydrocarbon mixture of the same composition at any
given time. The manner in which this is accomplished will be
discussed with respect to the particular views of the reactor
structure. A predetermined residence time for the hydrocarbon
mixture is provided. When that time is expired, valve 22 is moved
to a second position to connect port B with port C and port A with
port D. Meanwhile it is noted that valve 72 is shut off after
sufficient helium gas has been introduced to inject the hydrocarbon
sample from the coil 54 into the reactor.
To establish a rapid withdrawal of the reaction from the reactor,
this is accomplished by use of a source of vacuum generally
designated 74 which is controlled by valve 76 as connected to line
78 and 80 at T coupling 82. The valve 76 is opened to apply vacuum
to the lines and coil 84 and is then shut off. The vacuum coil 84
is at the same temperature as coil 54 in the range of 300.degree.
C. to 350.degree. C. depending upon the setting. Also, the coil is
at a very low pressure. By now moving the valve 22 to the second
position, vacuum as established in the lines is applied to the
reactor to immediately withdraw the reaction mixture through outlet
60 and via line 62 through ports B and C through line 86 into coil,
84. Due to the speed at which the reaction mixture is withdrawn
from the reactor, further transformation of the products evacuated
from the reactor are quickly and effectively stopped. In addition,
the controlled temperature in the heater box 18 is sufficiently low
in the range of 300.degree. C. to 350.degree. C. to stop further
reaction without risking condensing of products in a vacuum
coil.
Now that the reaction mixture has been removed and no further
reaction can continue, it is necessary to deliver the reaction
mixture from the coil 84 to the gas chromatograph 34. The
hydrocarbon sample is now located in the coil 84. The coil 84 is
then pressurized by helium gas supplied from the helium container
70. With the valve 22 in the second position with port A and D
interconnected and with ports 5 and 6 interconnected for the second
position of valve 20, the helium gas flows through valve 22 out
port D and through line 80 to the T coupling 82. With the vacuum
shut off, the pressurized helium pressurizes the coil 84 until the
pressure level in the reactor and auxiliary lines becomes very
close to the pressure of the thermal conductivity detectors in
system 24. Because of the direction of flow, the repressurization
provides extra assistance in purging any remaining hydrocarbon
product fractions from the reactor 12.
By switching valve 20 back to its first position with port 1
connected to port 5 and port 2 connected to port 6, the continuous
flow of inert helium is re-established through the reactor 12. The
hydrocarbon product sample, as located in line 62, circulates
through the set up via ports B and A as reconnected at position 1
for valve 22, through connected ports 2 and 6 of valve 20 via line
66 through the thermal conductivity detector 28 and into the gas
chromatograph 34. The gas chromatograph analysis is conducted using
a liquid nitrogen-cryogenic option in order to have the different
reaction products in a single chromatogram as specifically adapted
to analyzing the results of the cracking process.
As mentioned the test unit may also be used to test regeneration of
catalysts by introducing oxygen via the control valve 44 to
regenerate catalyst contained in the reactor 12. To accomplish
this, instead of using the feedstock injector system 16, the valve
44 is used to inject a predetermined quantity of oxygen into the
inert gas carrier line. With the valves 20 and 22 in the first
position, the oxygen injecting valve 44 is pushed to the load
position and a pulse of oxygen is introduced to line 48. After
contacting the catalyst for a preset time, that can range from two
to twenty seconds once the oxygen is introduced to the reactor 12
in the same manner as accomplished in introducing the hydrocarbon
sample via the coil 54, the products of combustion which are
primarily oxygen, carbon monoxide, carbon dioxide and water, are
evacuated from the reactor using the same method as described with
respect to removal of the hydrocarbon reaction products from the
reactor 12. The products of the coke combustion are analyzed in the
gas chromatograph 34 using a CARBOWAX (a trademark of Union Carbide
for a polyethlene glycol material) packed column. This type of
column provides an adequate separation for the combustion products
to evaluate the effectiveness of the regeneration process in
regenerating the catalyst.
The testing apparatus 10 provides a continuous flow of inert
carrier gas through the system to provide for a steady state
condition and then to inject a sample of reactant into the reactor
via the carrier gas. At that instance, flow of the carrier gas is
interrupted to provide for discontinuous operation of the system.
While the reactants are in the reactor, the system is monitored to
provide for a predetermined residence time at which point the
reaction mixture is rapidly withdrawn from the reactor. As noted,
one purpose of the system is to simulate reaction conditions in a
conventional catalytic riser reactor. Another object of the system
is to simulate the conditions in regeneration of spent catalyst. To
accomplish these aspects, the reactor 12 is specially designed to
provide at any instance during the residence time of the reactants
in the reactor an essentially constant concentration of reactants
in any portion of the reactor volume.
With reference to FIG. 2, the reactor 12 has a reactor chamber 88
defined by cylindrical interior surface 90. The reactor chamber 80
consists of an annular downflow zone 92 and an upflow zone 94.
These zones are defined by positioning a cylindrical annulus in the
reactor chamber 88. The cylindrical annulus 96 has a central core
98 extending vertically therethrough with the reactor in the
vertical orientation. The annulus 96 is supported by radially
extending cross-members 100. The annulus 96 is formed of a high
grade stainless steel, or other suitable metal which is not
reactive with the environment. The annulus is of considerable
thickness to provide a heat sink which maintains a constant
temperature for the fluidized bed of catalyst 102 within the core.
The bed of catalyst 102 is maintained in the upflow zone 94 by a
first screen 104 at the bottom opening 106 of the baffle. A second
screen 108 is positioned at the upper opening 110 of the baffle.
Either or both of these screens may be removable to permit
replacement of the catalyst 104.
To provide for the desired direction of circulation of inert gases
and introduced fluid reactants within the reactor chamber 88, a
circulating device in the form of a rotating impeller 1-2 is
employed. The intake region 114 of the impeller 112 is located
directly above the outlet screen 108 of the upflow zone. The
impeller 112 is provided with a plurality of vanes 116 as readily
attached to a hub 118 of the drive shaft 120 for the impeller. The
impeller is rotated at very high rpms in the range of 3000 and
above by driving the shaft 120 in the direction of arrow 122. For
example, the shaft speeds may range as high as 15,000 to 20,000
rpm. This causes a vigorous flow of the fluids in the reaction
chamber 88 by moving outwardly from the vanes 116 and downwardly in
the direction of arrows 124 and then upwardly through the upflow
zone in the direction of arrow 126. The impeller is thus rotated at
a sufficient speed to cause the fluids as they flow through the
upflow zone to fluidize the bed of catalysts 102 in the upflow zone
94. The volume defined between the inlet and outlet screens 104 and
108 is such to permit fluidization of the bed of catalyst without
over compression of same.
Due to the speed at which the impeller 112 rotates, there is a
tendency for a vortex to form in the annular downflow zone 92. This
is prevented by placing a plurality of radially extending baffles
128 about the outer cylindrical surface 130 of the annular baffle
96. This encourages a downwardly directed flow for the
recirculating reaction mixture. The volume of the reactor is such
that, by way of the vigorous, rapid recirculation of the reaction
mixture in the downflow zone and back into the upflow zone, there
is minimal time span between the time when the reaction mixture
leaves the outlet screen 108 until it returns to the inlet screen
104. This provides that at any moment during the residence time of
the reactants in the reactor, the concentration of the reactants is
essentially constant throughout the volume of the reaction chamber
88. This aspect simulates the conditions of a conventional
catalytic riser reactor. In that system, there is a contact time in
the range of two to twenty seconds where the reactants and the
catalyst flow together upwardly through the riser tube. At the top
of the tube, the catalyst is extracted from the reaction mixture by
way of cyclone devices in accordance with well known standard
techniques. With the reactor system of FIG. 2, essentially the same
conditions are achieved by providing this well mixed mini-fluidized
bed.
By locating the impeller 112 at the outlet of the upflow zone,
there is little if any tendency for the high speed rotation of the
impellers to cause inconsistencies in the miniaturized bed. Hence a
more uniform flow of the fluids through the fluidized bed of
catalyst is assured. To monitor the quality of the fluidized bed in
the upflow zone, two pressure taps are employed as shown in FIGS. 3
and 4. Minute bores 132 and 133 extend into the lower region 134
and into the upper region 140 of the reactor chamber 88. By
monitoring the pressure at these points in the reactor, it is
possible to determine the consistency of a fluidized bed throughout
the run of the testing device. The lower portion 134 of the reactor
chamber 88 has a radiused portion at 136 to direct the upward flow
of the reaction mixture in the direction of arrows 126 as shown in
FIG. 2.
The inlet 58 for the reactor is shown in FIG. 4 which extends
through the upper block portion 138 of the reactor into the upper
portion 140 of the reactor chamber. The outlet 60 for the reactor
also extends through the upper block 138 and communicates with the
upper portion 140 of the reactor chamber 88. Hence the reactants
are introduced and extracted at the tip portions of the impeller
blade 116.
The lower block portion 142 of the reactor carries the heater units
68 in the bores 144. An appropriate controller is provided to heat
the reactor to the desired temperature and maintain it at that
temperature. In providing such control, thermocouples are located
in bores 132 and 133 to monitor the temperature at all times in the
system. When it is desired, the reactor is assembled by clamping
the blocks 138 and 142 together by use of suitable mechanical
fasteners, clamps or the like. The interfaces 146 and 148 are
properly machined so as to provide a suitable seal for the reactor
chamber 88.
It is important to provide a suitable seal at the interface of the
impeller shaft 120 and the body of the upper block 138. The shaft
120 extends through bore 150 and is sealed in the region of 120a by
a packing 152. The packing is compressed by way of cap 154 bolted
to the packing retainer 156. A sleeve 158 compresses the packing
152 by bolting the flange 154 in place. Due to the high
temperatures of the reactor, cooling about the packing retaining
body is required to prevent heat from the reactor degrading the
packing. A cooling jacket 160 is provided through which cooling
water is circulated by inlet 162 and outlet 164. In addition, the
cooling ensures that the packing does not overheat during high
speed rotations of the shaft 120. In this manner, the reactor
chamber 88 is sealed in the region of the impeller as it extends
through the reactor block 138.
With this design for the reactor, the conditions of a conventional
catalytic riser reactor can be simulated. By suitable operation of
the valves 20 and 22 in the manner previously discussed which may
be either manually or computer controlled, the switching from
continuous flows through the reactor to a discontinuous residence
time of reactants in the reactor is readily achieved. This set up
therefore allows the monitoring of the amount of hydrocarbon
feedstock injected, the quality of the mixing in the reactor
vessel, the adequacy of the hydrocarbon injection and the
effectiveness of the product evacuation from the reactor by the
vacuum withdrawal system.
As is appreciated in the design of the test unit and use of
auxiliary components, it is desirable to minimize the dead spaces
between the exit of the reactor and the thermal conductivity
detectors in order to prevent the distortion of the injected
reactant pulse as well as of the eluded products extracted from the
reactor. The vaporization system in the injection system is adapted
to provide a very rapid vaporization of the hydrocarbon sample
prior to injection. The data acquisition system in the
microprocessor and gas chromatograph has the appropriate rate of
data sampling to monitor the hydrocarbon concentration transients
going and returning from the reactor.
For purposes of testing the hydrocracking of hydrocarbons, the
reactor is normally operated at a temperature in the range of
500.degree. to 750.degree. C. Hence the reactor must be built of a
non-reactive or inert metal which can withstand these temperatures
without distorting. A preferred composition of construction is a
nickel based material sold under the trademark INCONEL which is
available from Inco of Canada. A preferred dimension for the
reactor is an overall diameter of six inches with the height being
approximately three inches. The diameter of the basket cavity for
the fluidized bed of catalytic particles is approximately 1.75
inches. The height of the basket cavity is approximately 1.7
inches. The diameter of the reactor chamber 88 is approximately 1
inch.
Because of the rapid circulation of the reaction mixtures through
the reactor chamber, it is possible to use a catalyst to oil ratio
which corresponds with the standard catalyst to oil ratio used in
conventional catalytic riser reactors. In such conventional
systems, the catalyst to oil ratio is based on the flow of catalyst
to the flow of oil. Knowing what ratio is used commercially, it is
possible to use a corresponding ratio in the reactor system by way
of a ratio of the weight of catalyst to the weight of liquid
hydrocarbon introduced to the reactor system. Hence correspondency
in simulating reactor conditions in the test unit are readily
achieved.
As noted, the system is equally applicable to the regeneration of
catalysts. In conducting such tests, the reactor is normally run at
a temperature in the range of 650.degree. C, to 700.degree. C. to
provide for oxidation of the coke on the catalyst surface by the
injected predetermined quantity of oxygen into the inert carrier
gas.
The reaction mixture, as fed to the gas chromatograph/mass
spectrometer with capillary capabilities, is then analyzed to
determine the quantity and identity of the reaction products and
from this information, the overall effectiveness of the catalyst
for the particular reaction conditions in terms of temperatures,
C/O ratio and the like is determined. The residence time of the
reactants in the reactor is the same as in the conventional riser
reactor system, i.e. in the range of two to twenty seconds. Hence
this test system provides a very quick evaluation of feedstocks,
catalysts and other factors which should be determined in
optimizing the overall operation of an industrial scale riser
reactor system.
A difference, which the system of this invention which
distinguishes over other systems, is that the reactor with internal
recycle has an upward flow through the catalyst chamber and with
intense internal recycle, there is simultaneously achieved a small
fluidized bed of cracking catalyst. Gas flow in this direction is
established by locating the appropriate blower above the catalyst
bed insert. Suction is created across the bed and the gas flow is
directed down the draft tube annulus. The subsequent fluidization
of solids prevents coke profiles to be formed during cracking
reactions. By trapping a pulse injection of hydrocarbon feed in the
reactor and allowing reaction to occur under batch conditions, the
transformations which occur when catalyst and oil come into contact
in a riser are effectively simulated. Considering the total gas
volume in the reactor and the catalyst volume, then an equivalent
hold-up of solids, as in a riser may be defined. These catalyst
particles see a changing hydrocarbon environment with time in the
same manner flowing solids in a riser contact a hydrocarbon mixture
of changing composition, while circulating through the transport
line.
EXAMPLE 1
An experiment was conducted using the equipment of FIGS. 1 and 2. A
draft tube insert containing the central catalyst basket is held in
place by a ring support. Catalyst is held in the central tube by
2-20 .mu.m porous plates (screens). The centrifugal blower, which
is a six-blade impeller, is located at the top of the tube insert.
Total internal gas volume is 30 ml and total catalyst chamber
volume is 2 ml (13.5 mm diameter by 15 mm height). Cartridge
heaters located in the Inconel 600 reactor block provide the
necessary heat for securing close to constant temperature in the
reactor vessel. A motor-pulley system is used to drive the blower
and the shaft seal is kept cool by means of a water cooling
jacket.
Reactor temperature is monitored by 1/16" diameter thermocouples,
one in the catalyst bed which controls the heaters and one in the
annulus region. Pressure taps strategically located in the catalyst
chamber allow measurement of bed and grid pressure drops.
The operating procedure for the system involves injection of gas
oil to the reactor followed by the reaction period, then purging of
the reactor products into the valve box and finally sampling of
gaseous products to the GC. Initially before injection of gas oil
to the reactor, a steady flow of nitrogen was allowed to pass
through the reactor to purge and pressurize the reactor.
The impeller was rotated at 9000 rpm and an injection of gas oil
was made into the hot reactor. After the specified reaction time
period the reactor is evacuated. As soon as the reactor pressure
range gauge reached zero, the valve was repositioned to separate
any products left in the reactor, which could undergo further
cracking past the designated reaction time, from those in the purge
lines.
To avoid flooding of the gas chromatograph (GC) capillary column,
the total products from the reactor were not sampled at one time.
The sample loop was used to send small amounts of the gaseous
products to the GC.
After the sampling period, the catalyst was regenerated by
connecting a flow of 20% oxygen and 80% helium to the reactor and
allowing it to pass continuously through the reactor heated at
650.degree. C. The regeneration period lasted ten minutes to
provide near to complete combustion of coke. The reactor was then
allowed to cool to the cracking temperature under a steady flow of
nitrogen and the injection procedure repeated.
To test the performance of the riser simulator, a commercial
paraffinic gas oil was cracked over Octacat catalyst. The catalyst
was steamed at 766.degree. C. for 18 hours to produce an
equilibrium catalyst which resulted in a 37% reduction in surface
area from the fresh catalyst value of 230 m.sup.2 /g.
The cracking runs involved twelve experimental conditions combining
three different catalyst/oil ratios (3, 5 and 7), two reaction
times (5 and 10 seconds) and two temperature levels (500.degree. C.
and 550.degree. C.) as summarized in Table 1.
TABLE 1 ______________________________________ LIST OF THE 12
EXPERIMENTAL CONDITIONS USED Experimental Temperature Reaction
Condition (.degree.C.) c/o Ratio Time(s)
______________________________________ 1 500 7 5 2 500 7 10 3 500 5
5 4 500 5 10 5 500 3 5 6 500 3 10 7 550 7 5 8 550 7 10 9 550 5 5 10
550 5 10 11 550 3 5 12 550 3 10
______________________________________
At each condition, three repeat injections of gas oil were made,
the products from each injection being sampled three times to the
GC for analysis. The GC integrator report gave weight distributions
of the components and the gas oil yield was calculated by summing
components in the range of C.sub.13 and greater. The gasoline range
was based on a C.sub.5 to C.sub.12 cut and the light gases were
classified as C.sub.4 and smaller. The yields of these three lumps
were averaged for the total samples analyzed at each experimental
condition.
The conversion of gas oil against catalyst/oil ratio is shown in
FIG. 6 for the two temperatures levels and two reaction times used.
The following expected trends were observed:
at a constant reaction time and temperature, conversion decreased
with decreasing C/O ratio;
at a constant catalyst to oil ratio and temperature, conversion
increased with reaction time;
at a constant catalyst to oil ratio and reaction time, the
conversion also increased with temperature.
To visualize the effects of the operating variables (reaction time,
catalyst to oil ratio and temperature) on the lumped product
yields, three plots were made (FIGS. 7, 8 and 9). As expected, the
yield of gasoline increased with reaction time for the two times
considered, at constant catalyst to oil ratio and temperature. FIG.
7 shows that holding reaction time and temperature constant, the
yield of gasoline increased slightly with catalyst to oil ratio for
both reaction times.
At the higher temperature (550.degree. C.), the gasoline yields
were only slightly affected by variations in C/O levels for the two
reaction times considered as indicated by FIG. 8.
A more apparent effect on gasoline yield is that of temperature.
Comparing FIGS. 7 and 8, it can be observed that for both reaction
times, the gasoline yields at 550.degree. C. were lower than at
500.degree. C., for constant C/O levels. The largest decrease was
seen at the highest catalyst to oil ratio. This effect of
temperature on gasoline yield shows that for the catalyst tested,
the same type of trade-off normally involved in catalytic cracking,
between increased oil conversion and decreased gasoline yield at
higher temperatures, was an important factor.
FIG. 7 also compares the light gases plus coke yields with catalyst
to oil ratio at 5 to 10 seconds reaction time and a temperature of
500.degree. C. It is seen that as the C/O parameter increases so
does the yield in light gases and coke. The yields are larger at
the higher reaction time. Also, the slope of the yield versus
catalyst to oil ratio curve is larger for the light gases plus coke
product lump than for the gasoline product. This shows that, as
conversion is increased, the production of light gases plus coke is
increased to a greater extent than the gasoline yield.
The effect of temperature on light gases plus coke yield was that,
at the higher temperature (FIG. 8), the yields were higher and the
yield versus catalyst to oil ratio curve increased more sharply
than at 500.degree. C.
The selectivity to gasoline was defined as the ratio of the weight
of gasoline to the weight of light gases plus coke in the converted
products. FIG. 9 shows a plot of selectivity to gasoline versus
catalyst to oil ratio for the twelve experimental conditions. The
most significant effect is that of temperature. At a temperature of
550.degree. C., the gasoline selectivity is reduced by about 40% on
average as compared to that at 500.degree. C. Selectivity to
gasoline was also better at the lower catalyst to oil ratios,
although the increase was not so significant.
The assessment of the research octane number (RON) for the gasoline
fraction (C.sub.5 to C.sub.12) was performed using the method of
Anderson et al, J. Inst. Pet., 1972, 58, pp 83-94, who used a
multiple regression analysis to estimate the effective octane
numbers for groups of hydrocarbons.
The averaged values of the RON'S for the experimental conditions
used are tabulated in Table 2.
TABLE 2 ______________________________________ Research Octane
Number (RON) of the Gasoline Experimental Condition RON
______________________________________ 1 94.5 2 94.5 3 96.3 4 95.6
5 96.1 6 96.0 7 98.1 8 98.3 9 97.7 10 97.6 11 97.0 12 96.5
______________________________________ RON average for T =
500.degree. C. is 95.5 and RON average for T = 550.degree. C. is
97.5
The high values obtained indicate the selective capability of the
Octacat catalyst to form aromatics, branched hydrocarbons, and
olefins.
The effect of catalyst to oil ratio and reaction time on the RON
was small. Consistent trends were not observed for the range of
conditions used. Using a higher temperature, with catalyst to oil
ratio and reactive time held constant, increased the RON. For an
increase of 50.degree. C., the RON on average increased 2 numbers
from 95.5 to 97.5. This may be explained by slower hydrogen
transfer reactions compared to cracking rates at higher
temperatures resulting in increased olefin and aromatic content and
low paraffin content.
The simulation of fast catalytic cracking (FCC) reactions, as the
ones taking place in an industrial riser cracker, were found to be
effectively represented in a bench-scale reactor termed the riser
simulator.
The paraffinic gas oil cracked using Octacat catalyst showed
typical trends in product yields and gasoline research octane
numbers as those found in commercial FCC processes. As well, the
kinetic parameters obtained from the three-lump model were in the
range of literature values, although this comparison must be made
under close examination of the catalyst type and feedstock used for
each experiment. Also, the riser simulator model accurately
describes the cracking transformations without the volumetric flow
correction needed in flow reactor models. Subsequently, the molar
rate equations may be written in equivalent terms of weight
fractions allowing analysis of the kinetic parameters directly from
the GC analysis.
The wide range of operating conditions, such as reaction time,
temperature and catalyst to oil ratio, possible in the new rise
simulator makes it an effective tool for providing diverse kinetic
a=data for FCC processes. Although some fluid-dynamic
simplifications are apparent in the unit, a pilot-scale FCC
configuration (2-3 m length transfer line) is limited to a narrow
range of operating conditions set by the dimensions of the unit.
For example, the increase in space time in the tube reactor is
limited by the height of the tube, as determined by the choking
velocity for the unit. Considering these limitations and the
increased complexity and cost involved in a pilot-scale, then a
bench mark study, such as one that is conducted in the riser
simulator, is fully justified.
Another valuable use of the riser simulator is that which is
presently accomplished in industry by MAT test as previously
described. This test is effective on a comparative basis where
yield patterns of different cracked gas oils can be compared with
various catalysts. However, the ability to extrapolate the results
of MAT tests to commercial rise units and set with this data
appropriate kinetic models is uncertain, due to certain
inadequacies of the test (long catalyst times-on-stream and coking
profiles in the bed). The riser simulator, on the other hand, has
the ability to avoid these uncertainties and at the same time give
a quick comparison of hydrocarbon distributions for a given
catalyst-feedstock combination under a wide range of operating
conditions.
Although preferred embodiments of the invention have been described
herein in detail, it will be understood by those skilled in the art
that variations may be made thereto without departing from the
spirit of the invention or the scope of the appended claims.
* * * * *